Problem 9 - Biochemistry

Question

What is meant by the term "inborn errors of metabolism"? Give three examples of inborn errors that are directly related to the metabolism of phenylalanine and tyrosine.

Step-by-Step Solution

Answer

Short Answer: Inborn errors of metabolism are genetic disorders caused by a deficiency or dysfunction in an enzyme or transport protein, disrupting specific metabolic pathways in the body. Phenylalanine and tyrosine metabolism are essential for the production of neurotransmitters, hormones, and pigments. Three examples of inborn errors of metabolism related to phenylalanine and tyrosine are Phenylketonuria (PKU), Tyrosinemia Type I, and Alkaptonuria, which can cause severe health problems like mental retardation, liver and kidney damage, and tissue damage, respectively.

Step 1: Define Inborn Errors of Metabolism

Inborn errors of metabolism are a group of genetic disorders caused by a deficiency or dysfunction in an enzyme or transport protein that disrupts a specific metabolic pathway in the body. These are mostly inherited diseases, and often result in the accumulation of toxic substances or deficiency of needed compounds that can cause severe health problems or even death.

Step 2: Phenylalanine and Tyrosine Metabolism

Phenylalanine and tyrosine are amino acids that are essential components of proteins and involved in vital biochemical processes in the body. Phenylalanine metabolism begins with the conversion of phenylalanine to tyrosine, which is then further metabolized into other compounds. Both phenylalanine and tyrosine serve as precursors for the production of important neurotransmitters, hormones, and pigments in the body.

Step 3: Example 1 - Phenylketonuria

Phenylketonuria (PKU) is an inborn error of metabolism that occurs due to a deficiency of the enzyme phenylalanine hydroxylase (PAH), which is responsible for converting phenylalanine to tyrosine. In PKU, the absence of PAH causes phenylalanine to accumulate in the body, leading to severe mental retardation, seizures, and other neurological problems if not properly managed through a low-phenylalanine diet.

Step 4: Example 2 - Tyrosinemia Type I

Tyrosinemia Type I is an inherited metabolic disorder caused by a deficiency of the enzyme fumarylacetoacetate hydrolase (FAH), which is essential for breaking down tyrosine. This deficiency results in the accumulation of tyrosine and its toxic metabolites, leading to liver and kidney damage, neurological crises, and an increased risk of liver cancer.

Step 5: Example 3 - Alkaptonuria

Alkaptonuria is a rare inborn error of metabolism caused by a deficiency in the enzyme homogentisate 1,2-dioxygenase (HGD), which is involved in the degradation of tyrosine. The deficiency results in the accumulation of homogentisic acid, which polymerizes and accumulates in various tissues, causing them to darken. This leads to a condition called ochronosis, where joints and other connective tissues become brittle, and can result in arthritis, heart valve damage, and kidney stones among other problems.